As shown in FIG. 12, for example, a conventional electrostatic chuck 1 is employed as a part of a mounting body of a plasma processing apparatus in case of performing a plasma processing on a substrate (for example, wafer) W. Specifically, the electrostatic chuck 1 is used to attract and hold the wafer W on a top surface of the mounting body 2 by using an electrostatic force. Further, a focus ring 3 is disposed around a mounting surface of the mounting body 2 to surround the wafer W placed on the electrostatic chuck 1.
Moreover, a high frequency power supply 4 is connected to the mounting body 2 via a matching unit 4A. By applying thereto a predetermined high frequency power from the high frequency power supply 4 under a preset vacuum level, a plasma of a processing gas is generated between the mounting body 2 and an upper electrode (not shown), and the plasma thus generated is concentrated on the top surface of the wafer W by the focus ring 3. Formed inside the mounting body 2 is a coolant passageway 2A through which a coolant circulates to cool the mounting table 2, to thereby maintain the temperature of the wafer W at a predetermined level. Further, a gas channel 2B for a thermally conductive gas (for example, a He gas) is also formed inside the mounting body 2, wherein the gas channel 2B is opened at plural locations on the top surface of the mounting body 2.
The electrostatic chuck 1 is provided with through holes 1A corresponding to the gas channel 2B. The He gas supplied from the gas channel 2B is introduced into a gap between the mounting body 2 and the wafer W via the through holes 1A to thereby make a fine gap between the electrostatic chuck 1 and the wafer W become thermally conductive such that the wafer W can be efficiently cooled by the mounting body 2. The electrostatic chuck 1 is formed of, for example, sintered alumina or ceramic obtained by alumina thermal spraying, and an electrostatic plate 1B connected to a DC power supply 5 is embedded therein. The electrostatic chuck 1 attracts and holds the wafer W by using an electrostatic force generated by a high voltage applied from the DC power supply 5. Moreover, a plurality of vertically movable lifter pins (not shown) is installed in the mounting body 2 in order to perform loading/unloading of the wafer W onto/from the electrostatic chuck 1.
However, in case of an electrostatic chuck obtained by ceramic spraying, its wafer adsorption surface is weak, so that, for example, particles generated from the material of the wafer adsorption surface are likely to stick to a bottom surface of the wafer W, causing cross-contamination during a cleaning operation of the wafer W. Furthermore, the surface of the electrostatic chuck 1 may be roughened gradually as the adsorption and the separation process of the wafer W are repeated, and such a change in the surface state of the electrostatic chuck 1 makes it impossible to control the temperature of the wafer as in the initial stage. As a result, the temperature of the wafer gets changed with time.
Meanwhile, electrostatic chucks 1 formed of, e.g., sintered alumina are disclosed in, for example, Japanese Patent No. 3348140 (“Reference 1”) and Japanese Patent Publication No. 2000-332091 (“Reference 2”). Reference 1 discloses an electrostatic chuck featuring an improved corrosion resistance of a halogen based gas against a plasma while Reference 2 describes an electrostatic chuck provided with a multiplicity of dots on the surface thereof. Such electrostatic chucks can eliminate the above-mentioned problems.
In case of the electrostatic chuck disclosed in Reference 1, however, though the plasma resistance can be improved, there is a likelihood that, when the wafer W is separated from the electrostatic chuck by using lifter pins, the wafer W springs up by the lifter pins due to an attraction force of residual electric charges of the electrostatic chuck since the gap between the electrostatic chuck and the wafer W is narrow while the electrostatic capacitance of the electrostatic chuck is great, as in the case of the electrostatic chuck obtained by the ceramic spraying.
In case of the electrostatic chuck disclosed in Reference 2, since the multiplicity of dots are provided on the wafer adsorption surface, the problem of the wafer's springing up can be solved. However, the dots of the electrostatic chuck are of a low height of 5 μm or less, so that it is difficult to allow a thermally conductive gas to be uniformly distributed over the entire surface of the wafer W even though the thermally conductive gas is supplied into the gap between the electrostatic chuck and the wafer W. As a consequence, a rapid control of the wafer temperature cannot be realized. Moreover, though groove portions are radially provided on the surface of the electrostatic chuck in order to distribute the thermally conductive gas over the entire surface of the wafer W, there frequently occurs a difference in heat transfer between the groove portions and the other portions, making it difficult to uniformly control the in-surface temperature of the wafer. Furthermore, since the contact area of the dots and the wafer W amounts to about 20%, which is great, a desired temperature or a desired temperature distribution cannot be obtained by using the thermally conductive gas. Still further, it is not sure that this electrostatic chuck has a plasma resistance.